In a secondary battery device comprising an assembled battery including a plurality of secondary battery cells, the voltage of each secondary battery cell and the temperature of the assembled battery, for example, are monitored, so as to avoid dangerous states such as overvoltage.
Further, an assembled battery that uses a plurality of secondary battery cells in combination is generally known to cause unevenness in stored energy in the combined secondary battery cells due to variation in charge and discharge, temperature, and the like of the secondary battery cells.
When the energy stored in the secondary battery cells has become uneven, charge and discharge cannot be performed efficiently such that functions as an assembled battery are made best use of. Conventionally, a resistance discharge approach has been proposed, as a circuit that equalizes such energy.
The voltage correction circuit of the secondary battery, for example, judges unevenness in voltage or capacity of batteries and discharges by connecting a battery with a high energy to a resistance. The battery voltage correction device of the assembled battery, for example, performs a discharge operation so as to adjust the level before discharge. The conventional art proposes, for example, a battery group control device and a battery power system in which energy between unit cells is measured by an unloaded voltage, a remaining capacity of each of the unit cells is calculated, and a charge and discharge current is bypassed in a cell having a deviation greater than a set value with respect to a mean remaining capacity of the unit cells.
A secondary battery cell that equalizes energy (hereinafter referred to as “cell balance control”) comprises, for example, an assembled battery including a plurality of secondary battery cells, an equalization circuit configured to discharge the secondary battery cells, a switch control circuit configured to control the operation of the equalization circuit, and a control device (such as micro processing unit (MPU)) configured to control the monitoring operation of the voltages of the secondary battery cells, the operation of the switching control circuit, and the like. The control device is fed from an external power source provided outside.
In order to discharge a secondary battery cell having a high stored energy and control the cell balance of a plurality of secondary battery cells forming an assembled battery, a relatively long time will be required. Further, when the assembled battery charges a plurality of secondary battery cells, the voltages of the secondary battery cells need to be monitored.
When a control device configured to control the monitoring operation of the voltages of a plurality of secondary battery cells, the operation of the switching control circuit, and the like, is constantly activated, it is difficult to suppress consumption of external power source.
When the above-described secondary battery device is installed in a vehicle, it is necessary to control the cell balance even while the vehicle is parked. Accordingly, if feed from a battery designed for electrical components to a control device is continued, for example, during the cell balance control, it is difficult to suppress consumption of the battery designed for electrical components.
Further, since the cell balance control is designed to equalize the energy stored in another secondary battery cell in a secondary battery cell with the minimum voltage by discharging the secondary battery cell, the secondary battery cell may be overdischarged if the cell balance control is continued. Such a case should be avoided.
As a method of avoiding overdischarge of a secondary battery cell and protecting the secondary battery cell, there is a method of forcedly stopping the cell balance control when an instruction to continue the cell balance control is not given to the cell balance execution device for a predetermined period of time.
When the cell balance execution device is configured so as to forcedly stop the cell balance control, it is necessary to give an instruction to continue the cell balance control from the control device to the cell balance execution device periodically, during the cell balance control. Accordingly, it is impossible to stop feeding to the control device even when a vehicle installed with a secondary battery device is parked. In such a case, too, it is desired to reduce power consumption of secondary battery cells is desired.